The Myxobacteria are a group of Gram-negative bacteria that undergo a true multicellular development and a primitive differentiation. They provide a simple system for investigating the regulation of development because they resemble more familiar bacteria in structure and in their accessibility to genetic manipulation through mutation and gene cloning. Myxobacteria grow vegetatively like other bacteria, but when nutrients become limiting, Myxobacteria aggregate to form multicellular fruiting bodies. Within nascent fruiting bodies cells sporulate, changing - in the case of Myxococcus xanthus - from long rods to spherical spores, which are dormant. Under appropriate conditions, the spores germinate to give rod-shaped growing cells. Interactions between myxobacterial cells coordinate their development of fruiting bodies. The objective of the research proposed is to find out, in molecular and cellular terms, how this simple developmental process is regulated and how the cell-cell interactions coordinate development. The signal molecules that cells use when they interact with each other in the formation of fruiting bodies will be isolated and identified. For this purpose, a set of mutants that signal molecules, and the signal transduction system will be studied using these mutants and a transposable probe for promoter activity. In the long term, this research may facilitate the understanding of human developmental birth defects and speed their medical treatment. Cell-cell interaction are known to be important in human embryonic development and immunological interactions are difficult to investigate. In Myxobacteria the full power of biochemistry and molecular genetics can be used to study its cell interactions.